Nonflammable hydraulic fluid



A Patented May so, 1950 NONFLAMIHABLE HYDRAULIC FLUID Forrest J. Watson, Oakland, and Rupert 0. Morris, Berkeley, CallL, assiznors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application May 13, 1947, Serial No. 747,844

13 Claims. (Cl. 252-78) This invention relates to oleaginous compositions, and particularly to compositions suitable for use as hydraulic fluids and/or insulating oils. More specifically, the invention is concerned with nonflammable synthetic oils having excellent viscosity indices.

Mineral oils have for many years been universally used as bases for lubricants and for hydraulic fluids. This has been due in large part to the abundant supplies of petroleum and to the fact that with improved means of refinement, and through treatment with chemical .addition agents, it has been possible to modify or overcome some of the inherent properties of these oils which are undesirable for a number of purposes involving lubrication, electrical insulation, etc. The structural complexity of petroleum oils, and their relations of the chemical and physical properties are conducive to many problems in performance. have relatively poor viscosity indices. This property may at times be improved to a limited degree by the addition of certain materials which raise the viscosity index. From a safety standpoint, the flammability of petroleum products makes their use hazardous and undesirable, especially for such uses as hydraulic fluids to be used in aircraft equipment such as landing gear. Under normal operating conditions, petroleum oils are readily susceptible to deterioration through oxidation, which in turn usually causes sludge deposits and various corrosion difllculties.

Certain synthetic materials have been used to a limited extent to replace mineral oils for specific purposes. It is well known that chlorinated hydrocarbons have a reduced tendency toward flammability. However, the use of such compounds, especially for hydraulic fluids, has been largely unsatisfactory due to their serious corrosive characteristics. Furthermore, such compounds had too low viscosity indices for use in equipment subject to wide temperature variations. Liquids to be used for such purposes as hydraulic fluids must meet a series of stringent specifications if they are to be satisfactory, especially for use in aircraft: the fluid should be non-flammable, of extreme high viscosity index, substantially non-corrosive, and should possess a certain amount of extreme pressure properties.

It is an object of this invention to provide improved oleaginous compositions especially suit- For example, mineral oils generally.

able for use as hydraulic fluids. It is another object of this invention to provide improved fluids for use as transformer oils and other insulating purposes. It is a further object of this invention to provide improvedhydraulic fluids which are substantially completely non-flammable, noncorrosive, and of high viscosity index, and which at the same time possess satisfactory extreme pressure properties.

Now, in accordance with this invention, it has been found that normally liquid substantially completely halogenated carbon compounds form highly satisfactory compositions especially suitable for use as hydraulic fluids when used in the presence of a viscosity index improving agent, said agent being either a highly polymerized olefin or a polymerized unsaturated ester. Still in accordance with this invention, it has been found that such compositions may be greatly improved in regard to their corrosion characteristics by the addition thereto of certain corrosion inhibition agents, especially those selected from halogenated epoxides, unsaturated epoxides, cycloallphatic epoxides, metallic salts of aromatic acids, condensation of aldehydes with substituted phenols, and aromatic epoxides. It has also been discovered that the wear characteristics of the present compositions are greatly improved by the presence therein of a certain amount of mineral oil. Such inclusion may be made without changing the non-flammable characteristics of the composition as more fully described hereinafter. Furthermore, it has been found that certain limited classes of additives may be used in these compositions to improve their extreme pressure properties as more fully described hereinafter. Additionally, it has been discovered that these compositions may be favorably modified by the optional addition of a limited amount of partially halogenated organic compounds. Similarly, it has been found that the inclusion of substituted phenols, amino phenols or aromatic amines substantially improves the oxidation stability of the above compositions. The individual components of the subject composition will be discussed below.

Fully halogenated organic compounds The essential bases which comprise hydraulic fluids of the present composition are substantially completely halogenated organic compounds which are liquid at normal temperatures. By normal temperatures is meant temperatures varying from about 20- C. to about 200 C. These include chlorinated, brominated, iodinated and fiuorinated organic compounds, especially the fully halogenated lower hydrocarbons (whether saturated or unsaturated) wherein substantially all of the hydrogen atoms have been replaced by the same or different halogen atoms. The compound most suitable for use in the subject hydraulic fluid is hexachlorobutadiene. Other suitable bases for the present composition include hexachloropropylene, hexabrornopropylene, as well as their fully halogenated homologs and analogs. It has been found that in order to reduce flammability completely it is essential that such composition contain a preponderant amount of one of the above fully halogenated carbon compounds. Although partially halogenated organic compounds may be included in the composition, as hereinafter described, such inclusion must be accompanied by that of a fully halogenated compound in order to insure substantially complete non-flammability.

Viscosity index improving agents It was appreciated that mineral oils could be modified by a variety of substances in order to improve the viscosity indices thereof. However, it was found that the action of many of these modifying substances was specific to mineral oil alone and that for the most part such modifiers had substantially no effect upon the viscosity in dices of fully halogenated carbon compounds. However, it was discovered that two classes of substances form highly effective agents for the improvement of the viscosity indices of fully halogenated organic compounds, namely, highly polymerized olefins and polymerized unsaturated esters. Suitable polymerized olenns include polyisobutylene, polystyrene, polyindene, polymerized 1,3-butadiene and polyisoprene. The unsaturated esters whose polymers may be used to improve the viscosity index of the above syn-=- thetic hydraulic fluids include those in which unsaturated groups appear in the acid or alcohol portions of the ester or in both. However, the more satisfactory polymers for the present use are those obtained by polymerizing esters of run saturated acids, especially esteriiied methacrylic and more particularly, those in which the alcohol portion of the ester contains from about a to about 16 carbon atoms.

When these two types of agents are combined with fully halogenated carbon compounds there is a substantial and permanent increase in the viscosity index of the resulting composition. When used with mineral oil of medium properties such agents may improve the viscosity index thereof but only to a limited extent in the nature of to viscosity index points. When, however, these agents are employed with fully halogenated carbon compounds the increase in viscosity index may be as much as '75 or 100 Viscosity index points. Furthermore, this increase in viscosity index is of a permanent character.

As noted above, other agents believed to have viscosity index improving properties have been incorporated in the compositions described herein but for the most part have been found unsuitable usually because of their substantial lack of any favorable effect upon the viscosity indices of said compositions.

It has been found that the inclusion of from about 2 parts to about 15 parts of one or the other or both of these types of viscosity index improving agents per parts of fully halogenated carbon compound is satisfactory for the present purpose. Optimum results are obtained when 5 to 10 parts of the agent are used per 100 parts of the halogenated carbon compound.

Corrosion inhibitors One of the essential features of oleaginous compositions, especially when used for such purposes as hydraulic fluids or insulating oils is that they be of low, preferably negligible corrosivity. Especially when such compositions are employed as hydraulic fluids, it is an essential feature thereof that the corrosion characteristics be so low that the relatively moving parts of the hydraulic apparatus are not corroded during extended period of use. Any appreciable amount of corrosion whatsoever in a hydraulic apparatus such as landinggear might be fatal in its consequences to the safety of an aircraft and its passengers.

The high corrosion characteri tics of halogenated compounds in the presence of moisture is notorious. In the absence of modifying agents such compounds are definitely unsatisfactory for use in such delicate equipment as hydraulic apparatus. The great variety of corrosion inhibitors employed in petroleum compositions proved to be substantially unsatisfactory for the prevention of corrosion of the type occasioned by the contact of fully halogenated compounds with metallic surfaces, especially in the presence of moisture. The reason for this lack of corrosion prevention under such circumstances has not been fully elucidated but may be occasioned by the rapid consumption of ordinary mineral. oil corrosion inhibitors when employed with halogenated carbon compounds. Although the theory behind this difference in phenomena is not clear, six classes of substances have been discovered, in accordance with this invention, which act as potent corrosion inhibitors for fully halogenated carbon compounds. These include halogenated epoxides such as epichlorohydrin. Another highly satisfactory class of unsaturated corrosion inhibitors for halogenated compounds are the epoxides containing at least one unsaturated hydrocarbon group such as butadiene monoxide, and styrene oxide. A third type of satisfactory corrosion inhibitor includes the glycidyl cycloaliphatic ethcrs such as glycidylcyclohexyl ether and substituted derivatives thereof such as the alkylated glycidylcyclohexyl ethers. A fourth type of corrosion inhibitor for use in the present composition is the glycidyl aromatic ether such as glycidylphenyl ether and its alkylated derivatives, alkyl groups being substituted either in the glycidyl or on the aromatic radical. Two other types of corrosion inhibitors which substantially reduce the corrosion characteristics of fully halogenated carbon compounds are the condensates of aldehydes with phenols such as the condensates of formaldehyde such as para-octylphenol, and the metallic salts of alkylated aromatic acids such as zinc or magnesium disopropylsalicylate.

It has been found that from about 0.5 part to about 5 parts of one or more of the above corrosion inhibitors improve the corrosion characteristics of 100 parts of the fully halogenated carbon compounds to an unexpected extent, reducing the amount of corrosion caused thereby to a few per cent of that occasioned in their absence. Under normal operating conditions for such liquids as hydraulic fluids the inclusion of from 1% to 3% of the above corrosion inhibitors has been found to give satisfactory results.

Wear reducing components While the compounds of a fully halogenated carbon compound with one of the above described viscosity index improving agents provides compositions satisfactory for many purposes. it was. found upon investigation that such compositions tended to allow excessive wear when their prolonged'use was necessary. Furthermore, such compositions have a relatively high specific gravity and, since they are used in appreciable amounts in apparatus where weight is a factor such as in aircraft, it was desirable to reduce the specific gravity thereof, if such is possible without harming the characteristics of the hydraulic fluid. In order to reduce the specific gravity of fully halogenated hydraulic fluids containing one of the above viscosity index improving agents, a minor amount of mineral oil was added. As would have been expected, the specific gravity of the combination was that which had been easily calculated from the respective specific gravities of the components. However, in addition to reaching this predictable state. an entirely unexpected phenomenon was created by the combination, namely, the substantial reduction in the wear characteristics of the composition. By the inclusion of from about parts to about 40 parts of a mineral oil per 100 parts of the fully halogenated compounds, together with extreme pressure agents in the subject compositions it was found that the amount of wear occasioned during use was reduced to less than half of the value obtained in the absence of mineral oil. The addition of agents such as tricresylphosphate is especially desirable when mineral oil is pres- .ent.

A further accomplishment of this addition is the adjustment of the viscosity of these compositions to a desired degree for a specific purpose. Thus, mineral oils may be added having a suitable viscosity from about that of gas oil to about that of heavy lubricating 011, depending upon the viscosity of the composition which is required. When used in these amounts the flammability of the resulting composition is substantially that of the unmodified fully halogenated carbon compounds. As greater amounts than those specified above are employed the composition becomes more and more inflammable.

The mineral oils added to modify the wear characteristics, density and/or viscosity of the hydraulic fluids may contain any of the well known additives employed with mineral oil such as oxidationinhibitors, corrosion inhibitors, viscosity index improvers, pour point depressants,

wax suppressors, etc. Especially when the hy-- draulic fluid contains more than about parts of mineral oil per 100 parts of the fully halogenated carbon compound it is desirable to modify the oil with a viscosity index improving agent. Such agents may includes the two types specified above but any of the other well known types of viscosity index improvers may be used for this purpose.

Extreme pressure agents Mineral oils have been modified with a great variety of extreme pressure agents, most of which contain an active sulfur atom. However, it was discovered that for the most part such agents are not satisfactory for use with fully halogenated carbon compounds, especially when such agents contain an active sulfur atom. Although the reason for this is not clear, it appears that the halogenated compounds activate the sulfur in such a way that the latter becomes highly corrosive beyond that extent to which a satisfactory extreme pressure agent is normally employed.

It was discovered that there are two types of additives which may be employed in conjunction with fully halogenated carbon compounds so as to improve the extreme pressure property of the latter without inducing undesirable 'L 'lllOSiOll. These types are sulfurized animal or vegetable oils and organic phosphates. The first type is exemplified by sulfurized sperm oil and sulfurized castor oil, while the later includes trioctyl phosphate and tricresyl phospate as well as homologs and analogs. While the monoand di-substituted phosphates have extreme pressure properties in the subject compositions the trialkyl and triaryl phosphates are considered to be the more desirable. It has been found that the extreme pressure properties of the subject composition are improved to a satisfactory ex tent, especially for use as hydraulic fluids, by the inclusion of from about 3 parts to about 15 parts of one or both of the above types of agents per parts of the fully halogenated carbon compound. Under normal circumstances it is desirable to employ a minimum quantity of such agents, namely, from about 3 parts to about 6 parts thereof.

Partially halogenated organic compounds It is known according to past experience that other partially halogenated organic compounds contain a certain amount of non-flammability, but for maximum safety, such compounds can not be used as hydraulic fluids when substantially complete non-flammability is highly desirable. This is especially true of hydraulic fluids used in aircraft equipment. However, partially halogenated organic compounds and particularly partially halogenated hydrocarbons may be included in the composition if desired up to about 50 parts per 100 parts of the fully halogenated organic compound without appreciably impairing the flammability of the resulting composition. The most desirable types of halogenated hydrocarbons include the partially chlorinated aromatic hydrocarbons such as-partially chlorinated benzene, diphenyl, naphthalene or their derivatives such as alkylated, arylated. or alkyarylated aromatic hydrocarbons. Suitable examples of this variety include especially trichlorocumene, 2,2-dichlorophenol. 3,5-dichloronaphthalene, and 1,3-dichlorobenzene. If amounts of the partially halogenated hydrocarbons are increased by the limit set above the resulting composition becomes increasingly flammable and less suitable for uses where maximum safety is a major requirement.

Oxidation inhibitors While the compositions of the present invention ordinarily have satisfactory oxidation stabilization it has been found that the addition of substituted phenols, amino phenols, and aromatic amines, appreciably improve the stability of the composition especially when the latter are subject to attack by oxygen. Under normal conditions, such as in full enclosed hydraulic systems, hydraulic fluid is not subject to oxygen attack, but, for storage purposes and under more Tl stringent use the inclusion of 0.5-5 parts of the above types of inhibitors per 100 parts of fully halogenated organic compounds is desirable.

Recapitulating on the oleaginous compositions according to the present invention include the polymerized C4 to C9 unsaturated hydrocarbons and polymerized esters of C4 to Cm alcohols with an acid of the acrylic acid series, said polymer being present in an amount between improving polymer oi the group consisting of following ingredients: 5 2 and 15 parts by weight per 100 parts 01' said major ingredient. Com mm parts by 5. An hydraulic fluid according to claim 4 conweigh taming 0.5-5 parts by weight, per 100 parts of 100 said major ingredient, of a corrosion inhibitor r a compound m of the group consisting of halogenated epoxides, iii?fiieifiiif ifio tfiyiiirifi tdiiiiii 2-15 unsaturated epoxides, glycidyl cycloaliphatic g gigg g f Select from the group (Embed H ethers, glycidyl aromatic ethers, phenol-aldehyde Extreme pressure agentsasdcscribed above 0-15 COIIdEIISBJtBS, and metallic Salts Of alkylated aror zi r t i a li l ialogcnated organic compound 81% matic acids I ijexidotign Inhibitors .IIIIIIIIIIIIIIIII 0-5 i6 6. A substantially non-flammable hydraulic fluid consisting essentially of an organic com- In order to produce the most satisfactory hypound containing o Chlorine and Carbon atoms draulic fluid for use in closed substances the ioL- as the major ingredient thereof, S id Compound lowing composition is highly desirable: 233 q v trarilsg Of f om i 0 C. 1: 0 2o an a viscosi y n ex improv ng p0 fiexachlfmbutadfene merized ester of an acid of the acrylic acid series, of methacryhc said acid being esteriiied with a 64-016 alcohol, mmblt'or 'g said polymerized ester being present inan amount Mineral m1 1M between 2 and parts by weight per 100 parts Organic phosphate 3-15 at of said major ingredient.

The'iollowing examples are specific composi- I. A substantially non-flammable hydraulic tions especially useful as hydraulic fluids. Cer fluid consisting essentially of an organic comtain data accompany the compositions. The pound containing only halogen and carbon atoms wear test referred to in Example 5 is described as the major ingredient thereof, said compound by Boerlage in Engineering June 13, 1933. so being a liquid over the range C. to 200 0.,

Example 1 2 3 4- 5 Hexachlorobutadiene 9o so so 67.5 Hexachloropropylene 90 Chlorinated diphenyl 9 Poly (methacrylic ester) l0 l0 10 10 8. 5 Transformer mineral oil 19 Giyoidylcyclohexyl ether l Trioctyl phosphate. 10 6 Viscosity, cs. at 100 12.33 13.65 14.23 13.37 14.31 Viscosity Index 237 222 222 229 224 Pour Point, "F less than 65 less than -65 Wear test, mm. scar diameter" 0.36

We claim as our invention: and a viscosity index improving polymer 'of the 1. A substantially non-flammable hydraulic group consisting of polymerized C4 to C9 unsatflllid Consisting essentially the following urated hydrocarbons and polymerized esters oi gredient in sta y the S d Proportions: C4 to C16 alcohols and an acid of the acrylic acid Parts by weight, series, said polymer being present in an amount Hexachlorobutadiene 100 between 2 and 15 parts by weight per 100 parts Polymerized ester of methacrylic acid 245 of said major ingredient. Glycidyl cyclohexyl ether 0.5-5 8. A substantially non-flammable hydraulic Tricresyl phosphate 3-15 fluid according to claim '7 wherein the halogen A substantially non flammab1e hydraulic atoms of the major ingredient are selected from fluid consisting essentially of the following inthe group c s ing of fluorine and chlorine gredients in substantially the stated proportions: g b t t 11 n A su s an ia y nonammable hydraulic Hexachlombutadiene ff ffffif ifig d consisting essentially of t l wi in: Polymerized ester of methacrylic 245 gredients in substantially the stated proportions: Glycidyl cyclohexyl ether 0.5-5 Parts by weight Mineral oil 10-40 Hexachlorobutadiene 100 3. A substantially non-flammable hydraulic pqlymerized of methacrync 2-15 fluid consisting essentially of hexachlorobuta Mmeml on diene as the major ingredient thereof and from An extreme i i agent selected i 2 to 15 parts by weight, per 100 parts of hexa- 05 the F of Sulfunzed chlorobutadiene, of a viscosity index improving mal Sulfunzed Vegetable polymerized ester of methacrylic acid with an alky 1 p p afndatnary phosphate- 3-15 alcohol having from 4 to 16 carbon atoms. A cormslon i m selected from h 4. A substantially non-flammable hydraulic gr9up conslstmg of halpgenated fluid consisting essentially of an organic com- X1de'a.nm1atumted epoxlde aglycldyl pound containing only chlorine and carbon cycloallphatic ether, a glycidyl aromatic atoms as the major ingredient thereof, said ether a Phenolaldehyde condensate and compound being a liquid over the range of a metallic salt of an alkylated aromatic from 20 c. to 200" 0., and a viscosity index acid II 10. A substantially non-flammable hydraulic 9 fluid consisting essentially of the following ingredients in substantially the stated proportions:

Parts by weight Hexachlorobutadiene 100 Polymerized ester of methacrylic acid 2-15 Chlorinated diphenyl -50 Organic phosphate selected from the group consisting of a trialkyl phosphate and a triaryl phosphate 3-15 Metallic salt of an alkylated aromatic acid- 0.5-5

11. A substantially non-flammable hydraulic fluid consisting essentially of the following composition: 80 parts by weight hexachlorobutadiene, 9 parts by weight chlorinated diphenyl, 10 parts by weight of a polymerized ester of methacrylic acid and 1 part by weight of glycidyl cyclohexyl ether.

12. A substantially non-flammable hydraulic fluid consisting essentially of the following com position: 90 parts by weight hexachloropropylene and 10 parts by weight of a polymerized ester of methacrylic acid.

13. A substantially non-flammable hydraulic fluid consisting essentially of hexachlorobutadiene as the major ingredient thereof and from 2 to parts by weight per 100 parts of hexachlorobutadiene of a viscosity index improving polymer 0! the group consisting of (a) polymerized C4 to Co unsaturated hydrocarbons and (b) polymerized esters of C4 to C15 alcohols and an acid of the acrylic acid series, and 0-50 parts by weight per parts of hexachlorobutadiene of chlorinated dlphenyl.

FORREST J. WATSON.

RUPERT C. MORRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,082,528 Hunter Dec. 30, 1913 2,017,089 Cox Oct. 15, 1935 2,102,825 Woodhouse et al. Dec. 21, 1937 2,408,983 Kollen Oct. 8, 1946 2,413,170 Clark Dec. 24, 1946 2,423,927 Burke et al. July 15, 1947 2,438,446 Leland Mar. 23, 1948 FOREIGN PATENTS Number Country Date 418,230 Great Britain Oct. 22, 1934 

1. A SUBSTANTIALLY NON-FLAMMABLE HYDRAULIC FLUID CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN SUBSTANTIALLY THE STATED PROPORTIONS: 